Sometimes costs can be shared.  Also, one does not have to meet at hotel EVERY time one gets together, assuming that the couple are meeting more frequently than the minimum necessary for sexual encounters.  

Sometimes my paramour and I meet in a park for long lunch.  Sometimes I bring the lunch, sometimes he does.  We work together because for the two of us being together is more important than who pays and we find a balance for the paying of most things.

I earn more than he does and I control all of my own finances without interference by my husband and without his need to know what I am doing.  My lover, on the other hand, creates a budget with his wife and they work on their finances completely openly with one another, so money cannot easily go "missing," without her knowing.  Nevertheless, Brogan manages to save a little each week to contribute to the expenses of our affair.  

In order for him to feel more comfortable with our situation, we also reached a "gift" compromise, as I am a very generous person.  I can buy him gifts, so long as they don't cost more than $5.00.    It's amazing what one can get for $5.00...well sometimes I have gone over by a dollar!  In this way, he does not feel uncomfortable about the financial disparity between us.

Working together to find a way to make the affair possible is the best way to ensure the longevity of it.